In a sea of tower defense games on the iTunes App Store, Sentinel series stands alone. It's not because the gameplay is that unique because it isn't. The Sentinel series of games follow the traditional tower defense gameplay formula: your enemies come in on set paths and you must build enough towers to kill them and stop the deadly march. What makes the series so unique is the wonderful imagination of the developers that has created a Sentinel world like no other. The playing field is decidedly fantasy genre, towers are well designed with a wide variety and above all the alien enemies look like nothing you?ve seen in a tower defense game before.

Sentinel 3: Homeworld feels like an extension of Sentinel and Sentinel 2 with ample new maps and a new interface that provides upgrades to your commanders and ship weapons. If you?ve never played a Sentinel game, you are in for a treat. If you are already a fan of Sentinel and Sentinel 2, the third installment gives you something new to gawk at but keeping the familiar gameplay and look and feel of the last two games.

Gameplay

Although the three Sentinel games are all supposed to set on different planets (Mars, Earth and now aliens? home world), the environment doesn?t look much different in Sentinel 3 from the previous two games. You get the post apocalyptic, broken down factory plant surroundings with broken walls, shaky bridges and industrial waste pools to boot. Where there is a solid space, like a boulder, a roof of generators, etc., that?s also next to the path of the enemy invasion, you can build towers to destroy those who dare to go near. After playing the first Sentinel games, you will know immediately what to do in Sentinels 3: Homeworld. For the uninitiated, the first level in Campaign mode walks you through the basics of the gameplay.

There are plenty new content to warrant the new installment as a full game with 20 new Campaign levels, 16 endless levels and 6 Classic levels. And each of these levels has four difficulty settings that change the pace of the gameplay dramatically. Like in previous Sentinel games, the Campaign missions let you unlock maps for Endless mode and unlock weapons with each level you climb. The ground towers have some overlapping with previous Sentinel games; this means you still get to use your favorites like Laser, Bomb, Beam, Slow, Sniper towers and more. There are also some new towers as well, like Flame Thrower, Aerial Slow and more. Ship weapons too have new types like resurrection for your commander, attack drones and repair beam.

While some weapons look familiar to veteran players, the menu system is brand new. After each level you?ve completely (win or loose), you get to see your experience points, levels, credits and more. And you now have to buy each slot for the new weapons you?ve unlocked as well commander?s abilities. Slots for both ground tower and ship weapons get increasing expensive, which means you will likely have to replay the levels to earn enough for all the expenses to equip with best gear. The menu system is very intuitive and easy to use.

Aside from the new towers and ship weapons, the commander gets some shiny new abilities too, as well as an RPG like status upgrade. With advancing levels, the commander gets experience points also, and you can allocate them to increase his health, strength, shoot damage and morale. The developers did a great job making the commander upgrades relevant, as you go higher in levels, his abilities and effectiveness will shape the outcome of the level especially with boss enemy units. And yes you get your favorite aliens back too in Sentinel 3. Most alien enemy units stay the same as the last games with boss units peppered in between waves. In the advance levels of Campaign mode and Endless mode, you will get the boss more frequently.

Graphics & Sound

One of the things that made the Sentinels series one of the best tower defense series for the iPhone is the graphics. They have their own unique style, rugged terrain at the first glance but when you zoom in everything looks sharp. The turret design and alien unit design give life to this alien world that also look very familiar to us. Each turret has its own flashy explosions or beams and they work flawlessly and smoothly even when you cramp a bunch of them or a full screen of them in. Enemy units too show the incredible creativity of the designers. They come in different speed and shape (ground or winged), with different functions and purpose. The balance of these units also strikes a perfect note. You have to build different turrets to take care different types of enemies, and use your commander and ship weapons wisely. The graphics in Sentinel 3 look sharp and flashy.

Sentinel 3 offers sound tracks and special effects. If you like the sound tracks in Sentinel 2, you will get more of them in Sentinel 3 as they share the same creator. Like in the last Sentinel game, BMG in Sentinel 3 has a distinctive rhythm that goes from slow and light to frantic and busy beat. The arrangement eliminates the boredom of listening to the same type of tracks for a long time. If you wish you can use your own iPod music to company the long journey that Endless mode brings you. Sound effects are largely unchanged. You can turn audio of BGM and sound FX off and change volume separately

Conclusion

After hours of gameplay, Sentinel 3: Homeworld still feels fresh with plenty left to do. The large number of levels combined with three game modes and 4 difficulty levels give this game a huge replay value, though it will take you a long time to just complete the Campaign missions. Learning the power of new weapons, especially the new ship weapons and commander upgrade is a lot of fun even for Sentinel veteran players. If you are a tower defense player, Sentinel 3: Homeworld is not to be missed.